Buoyancy device

ABSTRACT

A buoyancy device ( 1 ) is attached to a structure to be floated or sunk. The buoyancy device ( 1 ) comprises a restriction device such as a rigid tube ( 3 ) and an inflatable member ( 5, 15 ) located within the restriction device ( 3 ). The restriction device ( 3 ) restricts inflation of the inflatable member ( 5, 15 ). The inflatable member ( 5, 15 ) comprises a first flexible portion ( 5 ) and may be in the form of a tube ( 5 ) and a second flexible portion ( 15 ) which may be in the form of a diaphragm ( 15 ). The tube ( 5 ) is coupled to the restriction device ( 3 ) and the diaphragm ( 15 ) is coupled to the tube ( 5 ).

[0001] The present invention relates to a buoyancy device particularly, but not exclusively, for attachment to large structures requiring to be lifted, lowered, positioned and transported via the ocean.

[0002] Conventionally, when an offshore drilling structure comes to the end of its working life, it is decommissioned. In the past, it was thought that decommissioning could entail sinking the drilling structure at the point where it once stood.

[0003] However, amongst other factors, environmental factors have recently increased the need for offshore drilling structures to be moved to shallower and calmer waters, or back on land so that the drilling structures can be dismantled safely.

[0004] Previously, moving the drilling structures has involved the use of flat back barges, onto which the drilling structures are hauled. However, these barges are expensive and costly in terms of manpower requirements.

[0005] Our previous PCT Publication Nos. WO 97/43172 and more particularly WO 00/29285 concern types of buoyancy devices upon which the present invention seeks to improve, and the disclosure of both WO 97/43172 and WO 00/29285 is incorporated herein by reference.

[0006] According to a the present invention, there is provided a buoyancy device for attachment to a structure to be floated or sunk, the buoyancy device comprising a restriction device and an inflatable member located substantially within the restriction device, such that the restriction device restricts inflation of the inflatable member, characterised in that the inflatable member comprises a first and second flexible portions, the first portion being coupled to the restriction device and the second portion being coupled to the first portion.

[0007] The second portion may be a bag, a diaphragm or a bladder, and the first portion may be a bag and more preferably is a cylindrical bag. Preferably the first portion or cylindrical bag is open ended at both ends and is preferably coupled to the restriction device at both of its ends.

[0008] Preferably, the restriction device permits the ingress and/or egress of fluid from within the buoyancy device, and typically, the restriction device has at least one aperture to permit fluid to flow therethrough. Typically, the buoyancy device is arranged such that water located outwith the restriction device can enter at least a portion of the restriction device and act upon the surface of the first and second portions.

[0009] Typically, the restriction device is of a substantially tubular nature, and is preferably open ended at both ends.

[0010] Preferably, one end of the first portion is secured to one end of the restriction device, and typically, the said one end of the first portion is coupled to a first fluid inlet and/or outlet port, and which may be a gas, such as pressurised air inlet/outlet port.

[0011] Typically, the other end of the first portion is secured to the other end of the restriction device, and typically, the said other end of the first portion is coupled to a second fluid inlet and/or outlet port, and which may permit water from outwith the buoyancy device to pass therethrough.

[0012] The first and second portions are preferably formed from a substantially flexible material, and the restriction device is preferably formed from a rigid material.

[0013] Preferably, an end of the second portion is secured to the first portion at substantially the mid-point of the interior of the first portion, and typically, one face of the second portion is in fluid communication with the said one end of the restriction device and hence the first fluid inlet and/or outlet port. Preferably, the other face of the second portion is in fluid communication with the said other end of the restriction device and hence the second fluid inlet and/or outlet port.

[0014] The diaphragm or bladder is preferably formed from a substantially flexible material, and the restriction device is preferably formed from a substantially rigid material. Typically, the first portion is secured to the second portion by welding and the first portion is secured to the restriction device by means of a pair of annular rings, which preferably comprise bores to provide the first and second fluid inlet and/or outlet ports.

[0015] Preferably, the first portion is substantially tubular when inflated, and the second portion is substantially semi-circular or dome-shaped when inflated.

[0016] Typically, the first portion is restrained at substantially all points along its longitudinal axis by the restriction device when inflated, and the second portion is restrained at substantially all points along its longitudinal axis by the first portion and the restriction device when inflated.

[0017] Typically, the buoyancy device may be operated between three configurations:

[0018] a) a non-inflated configuration;

[0019] b) a water inflated configuration; and

[0020] c) a gas inflated configuration.

[0021] Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which;

[0022]FIG. 1 is a schematic side view of a buoyancy device in accordance with the present invention;

[0023]FIG. 2 is a schematic side view of a flexible joint of the buoyancy device of FIG. 1;

[0024]FIG. 3 is a schematic side view of the buoyancy device of FIG. 1 prior to inflation with any fluid;

[0025]FIG. 4 is a schematic side view of the buoyancy device of FIG. 3 after inflation of the buoyancy device with air;

[0026]FIG. 5 is a schematic side view of the buoyancy device of FIG. 4 after evacuation of the air and the inflation of the buoyancy device with water;

[0027]FIG. 6 is a schematic side view of the buoyancy device of FIG. 1 showing the three different configurations thereof as shown previously in FIGS. 3, 4 and 5 combined; and

[0028]FIG. 7 is a schematic side view of the outer and inner bag of the buoyancy device of FIG. 1 in the configuration shown in FIG. 4.

[0029]FIG. 1 shows a buoyancy device 1 which may be arranged in any suitable arrangement, such as that shown in FIG. 12 of WO 00/29285 and hence which may be attached in a substantially vertical orientation to legs of an offshore drilling structure requiring to be lifted from the ocean floor and moved to a remote location.

[0030] However, it should be noted that the buoyancy device 1 may be attached in any suitable arrangement to objects other than offshore drilling structures, such as large ships, super tankers, cruise liners, etc. which may be required to be lifted in order to allow them to clear the open-sea end of dry docks.

[0031] A clamping device, similar to the clamping device 207 of WO 00/29285 may be used to clamp around a suitable number of buoyancy devices 1 of the present invention to attach them to the structure to be moved.

[0032] The buoyancy device 1 comprise a rigid outer hull 3 which may be formed from suitable material such as glass reinforced plastic (GRP), carbon fibre or any other suitable material; it should be noted that GRP is preferred.

[0033]FIG. 3 shows the buoyancy device prior to inflation with either water or air; the outer bag 5 (shown in long dotted lines) is substantially cylindrical in nature and, when deflated, can be thought of having substantially the same shape as a windsock. The outer bag 5 is coupled to the outer shell 3 at both ends 5A, 5B by means of an adapter ring flange 7. It should be noted that the “wet” end 5B of the outer bag 5 is open to the outer environment, such that sea water can pass into the interior of the outer bag 5 via the opening or bore 14B in the annular flange 7B. An anti-extrusion sieve plate 9B is formed across the end 5B and is arranged such that it permits water to pass through itself, but prevents the passage of other unwanted solid material into the interior of the outer bag 5. A similar anti-extrusion sieve plate 9A is located across the other end 5A of the outer bag 5.

[0034] The “dry” end 3A of the outer shell 3 and the outermost end of the adapter flange 7A, are coupled to a shell closure plate 10 which provides rigidity to the dry end 3A. An aperture 12 is provided at the centre point of the shell closure plate 10 and an air line 11 is secured to the aperture 12 via a valve 13, such that pressurised air can be introduced into the bore 14 of the adapter flange 7A by opening the valve 13. The air line 11 is coupled to a compressor which provides the pressurised air. In this manner, air can be introduced into the interior of the outer bag 5.

[0035] An inner half bag 15 or diaphragm 15 is secured around the diameter of the middle of the outer bag 5 and a suitable fixing is shown in the form of a flexible joint in FIG. 2.

[0036] Both the outer bag 5 and the diaphragm 15 are preferably formed from a suitably strong and flexible material or fabric and a most preferred material is polyester coated with a plasticised PVC which may have a weight of in the region of 900 mg per square metre. A suitable example of such a material is sold under the Trade Mark DURASKIN(^(RTM)).

[0037] The joint 17 is preferably formed by using known and conventional welding techniques to weld mid-pieces 19, 21 to the outer bag 5 and the diaphragm 15. Indeed, the welding process makes the joint 17 or hinge 17 stronger than the outer bag 5 or diaphragm 15 alone. Accordingly, the joint 17 will act as a soft flexible hinge to permit the diaphragm 15 to move from the configuration shown in FIG. 1 to the configuration shown in FIG. 4 and all points in between, including the non-inflated configuration shown in FIG. 3.

[0038] Prior to introduction of the buoyancy device 1 into water, the outer bag 5 and diaphragm 15 will take up a configuration something akin to that shown in FIG. 3. However, when the buoyancy device 1 is introduced into water, the water will flow into the interior of the outer bag 5 and will move the outer bag 5 toward the inner surface of the outer shell 3. At the same time, the diaphragm 15 will move from right to left as shown in FIG. 3 until it takes up the configuration as shown in FIG. 1. The air that was previously in section A (as shown in FIG. 3) of the interior of the outer shell 3 is able to escape through a pair of non-return valves 23, 24 provided in respective adapter rings 7A, 7B. Therefore, the non-return valves 23, 24 communicate with the interior of the outer shell 3 to permit air to escape the interior. However, the non-return valves 23, 24 prevent air from passing through themselves in the direction from outside the outer shell 3 to inside Section A of the interior of the shell 3.

[0039] The anti-extrusion sieve plate 9A also has the important task of preventing the diaphragm 15 from over inflation, that is, passing into the bore 14 of the adapter ring 7A.

[0040] When the time has come to inflate the buoyancy device 1 to aid in lifting a structure to be moved in the water, the valve 13 is opened and pressurised air will enter into bore 14 and hence into the interior of the outer bag 5. Since the joint 17 also provides a seal between the outer bag 5 and the diaphragm 15, the pressurised air in Section B (see FIG. 3) will cause the diaphragm 15 to move from left to right as shown in FIG. 1 until it takes up the fully inflated configuration shown in FIG. 4. It is thought that the working pressure of the buoyancy device 1; that is the pressure of the air within the buoyancy device 1; will be in region of 2.5 atmospheres, although it is likely to be operable up to in the region of 6 atmospheres or higher.

[0041] The anti-extrusion sieve plate 9B also has the important task of preventing the diaphragm 15 from moving into the bore 14B of the flange 7B.

[0042] Accordingly, the main purpose of the outer bag 5 is to provide a reasonably flexible mounting point for the joint 17 and diaphragm 15. Those skilled in the art will appreciate that the advantage provided by such a flexible joint 17 is that there is a far reduced risk of localised stresses building up in the wall of the outer shell 3.

[0043] It should also be noted that FIGS. 1 to 7 are not to scale. Indeed, the outer shell is in the region of 16 m in length and approximately 2.3 m in diameter.

[0044] Modifications and improvements may be made to the foregoing without departing from the scope of the invention. 

1. A buoyancy device (1) for attachment to a structure to be floated or sunk, the buoyancy device (1) comprising a restriction device (3) and an inflatable member (5, 15) located substantially within the restriction device (3), such that the restriction device (3) restricts inflation of the inflatable member (5, 15), characterised in that the inflatable member (5, 15) comprises a first (5) and second (15) flexible portions, the first portion (5) being coupled to the restriction device (3) and the second portion (15) being coupled to the first portion (5).
 2. A buoyancy device (1) according to claim 1, wherein the second portion (15) comprises a diaphragm (15).
 3. A buoyancy device (1) according to either claim 1 or 2, wherein the first portion (5) comprises a cylindrical bag (5).
 4. A buoyancy device (1) according to claim 3, wherein the cylindrical bag (5) is open ended at both ends (5A, 5B).
 5. A buoyancy device (1) according to claim 4, wherein the cylindrical bag (5) is coupled to the restriction device (3) at both of its ends(5A, 5B).
 6. A buoyancy device (1) according to any preceding claim 1, wherein the restriction device (3) permits the ingress and/or egress of fluid from within the buoyancy device (1).
 7. A buoyancy device (1) according to any preceding claim 1, wherein the restriction device (3) has at least one aperture (9B, 14B) to permit fluid to flow therethrough.
 8. A buoyancy device (1) according to any preceding claim 1, wherein the buoyancy device (1) is arranged such that water located outwith the restriction device (3) can enter at least a portion of the restriction device (3) and act upon a surface of the first (5) and second portions (15).
 9. A buoyancy device (1) according to any preceding claim 1, wherein the restriction device (3) is substantially tubular.
 10. A buoyancy device (1) according to claim 9, wherein the restriction device (3) is open ended at both ends (3A, 3B).
 11. A buoyancy device (1) according to claim 10, wherein one end (5A) of the first portion (5) is secured to one end (3A) of the restriction device (3), and the other end (5B) of the first portion (5) is secured to the other end (3B) of the restriction device (3).
 12. A buoyancy device (1) according to claim 11, wherein the said one end (5A) of the first portion (5) is coupled to a first fluid inlet and/or outlet port (7A, 14A).
 13. A buoyancy device (1) according to either of claims 11 or 12, wherein the said other end (5B) of the first portion (5) is coupled to a second fluid inlet and/or outlet port (7B, 14B).
 14. A buoyancy device (1) according to claim 13, wherein the second fluid inlet and/or outlet port (7B, 14B) permits water from outwith the buoyancy device (1) to pass into the buoyancy device (1).
 15. A buoyancy device (1) according to any preceding claim 1, wherein the first (5) and second (15) portions are formed from a substantially flexible material, and the restriction device (3) is formed from a rigid material.
 16. A buoyancy device (1) according to any preceding claim 1, wherein an end of the second portion (15) is secured to the first portion (5) at substantially the mid-point of the interior of the first portion (5).
 17. A buoyancy device (1) according to claim 12, or to any of claims 13 to 16 when dependent upon claim 12, wherein one face of the second portion (15) is in fluid communication with the first fluid inlet and/or outlet port (7A, 14A).
 18. A buoyancy device (1) according to claim 17, wherein another face of the second portion (15) is in fluid communication with the second fluid inlet and/or outlet port (7B, 14B).
 19. A buoyancy device (1) according to any preceding claim 1, wherein the first portion (5) is secured to the second portion (15) by welding and the first portion (5) is secured to the restriction device (3) by means of a pair of annular rings (7A, 7B).
 20. A buoyancy device (1) according to claim 19, wherein the pair of annular rings (7A, 7B) comprise bores (14A, 14B) to provide the first (7A, 14A) and second fluid inlet and/or outlet ports (7B, 14B).
 21. A buoyancy device (1) according to any preceding claim 1, wherein the first portion (5) is substantially tubular when inflated, and the second portion (15) is substantially semi-circular or dome-shaped when inflated.
 22. A buoyancy device (1) according to any preceding claim 1, wherein the first portion (5) is restrained at substantially all points along its longitudinal axis by the restriction device (3) when inflated, and the second portion (15) is restrained at substantially all points along its longitudinal axis by the first portion and the restriction device (3) when inflated.
 23. A buoyancy device (1) according to claim any preceding claim 1, wherein the buoyancy device (1) may be operated between three configurations: a) a non-inflated configuration; b) a water inflated configuration; and c) a gas inflated configuration. 